1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to a digital broadcast reception, and more particularly, to efficiently selecting a demodulation scheme for a particular channel in a digital broadcast receiver supporting a plurality of demodulation schemes.
2. Description of the Related Art
A digital broadcast receiver is an apparatus that restores original digital data from a broadcast signal transmitted according to a digital transmission scheme. A digital broadcast transmitter, i.e., a broadcast station area (hereinafter, referred to as a “head end”) converts an analog signal into a digital signal comprised of 0's and 1's using digital technology, compresses the converted signal together with other information, and then transmits the compressed signal according to a digital transmission scheme. Then, the digital broadcast receiver receives and converts the transmitted signal into original video and audio.
Compared to analog technology, digital technology is usually robust to noise, needs less transmission power, allows use of error correction, and has less degradation in transmission, copy, and accumulation. In addition, digital technology enables high band compression on a video/audio signal and facilitates search, processing, and editing of information. Digital broadcast using such digital technology is advantageous in that it is robust to noise and realizes efficient information transmission compared to conventional analog television (TV).
To transmit a digital broadcast signal through cable, terrestrial, or satellite propagation, modulation of a baseband signal such as an original video/audio signal is needed. Examples of digital modulation are quadrature amplitude modulation (QAM), quadrature phase shift keying (QPSK), and coded orthogonal frequency division multiplexing (COFDM). Of those, QAM is usually used for cable broadcast. Different formats of QAM, e.g., QAM64, QAM256, and QAM1024, have been commercialized. QPSK is used for a return channel in the cable broadcast. COFDM is used for terrestrial broadcast in Europe and for microwave multipoint distribution services (MMDS).
QAM is widely used in diverse fields including the field of cable broadcast. QAM uses an intermediate frequency (IF) modulation scheme of generating a QAM signal by modulating the amplitude of two quadrature carriers and two independent baseband signals. QAM is used to modulate digital information in a convenient frequency band. If the QAM scheme is used, a spectrum band taken up by a signal is matched with a pass band of a transmission line so that the signal is subjected to frequency division multiplexing or can be radiated using a small antenna. QAM is adopted by Digital Video Broadcasting (DVB), Digital Audio Visual Council (DAVIC), and Multimedia Cable Network System (MCNS) partners to transmit a digital TV signal through a coaxial cable, a Hybrid Fiber Coaxial (HFC) cable, a Microwave Multipoint Distribution System (MMDS) TV network.
The QAM scheme may be present in variable (4, 16, 32, 64, 128, 256, 512, and 1024) levels providing 2, 4, 5, 6, 7, 8, 9, and 10 Mbits/s/MHz. In this situation, a maximum of about 42 Mbits/s (QAM-256) can be provided through a United States CATV channel of 6 MHz and a maximum of 56 Mbits/s can be provided through a European CATV channel of 8 MHz.
Meanwhile, terrestrial broadcast in the United States adopts an 8-level vestigial side band (8-VSB) as a standard and has trended to a 16-level VSB (16-VSB). VSB technology is critical transmission technology for receiving a digital broadcast transmission signal and restoring compressed digital data to an original video/audio in a digital TV. The VSB technology is adopted as a terrestrial digital TV transmission standard in the United States, Canada, Korea, Taiwan, etc. Advanced Television System Committee (ATSC) has been developed from an analog system, National Television System Committee (NTSC). ATSC is a system in which NTSC is implemented in a digital mode at the same frequency bandwidth of 6 MHz as used in NTSC broadcast technology.
ATSC uses a VSB modulation scheme, in which video reception is possible if a signal level is at least 15 dB higher than a noise level when any interference signal like ghost is not present and a wide service area can be secured with small output power. In addition, ATSC is robust to impulse noise occurring in a spark-plug of an automobile or a motor of an electric fan, a drier, or the like.
A VSB system is mainly characterized by using a small pilot instead of a suppressed carrier used in QAM. The pilot is located on a Nyquist slope of an NTSC spectrum to minimize co-channel interference affecting NTSC broadcast. If there is no other channel corruption, a pilot signal can be received at a signal-to-noise ratio (SNR) of 0 dB and can also be easily received even under a poor condition like ghost or co-channel interference.
Examples of a commercialized VSB are 8-VSB and 16-VSB. While 8-VSB allows one digital broadcast program to be transmitted in a broadcast band, 16-VSB, i.e., digital cable TV transmission technology, allows two digital broadcast (i.e., HDTV) programs to be simultaneously transmitted in the same broadcast band. Accordingly, 16-VSB has been evaluated as efficient digital broadcast transmission technology in a cable TV broadcast environment.
As described above, most countries use a single designated modulation scheme (i.e., a broadcast standard) according to standards. Thus, a digital broadcast receiver performs demodulation according to a designated scheme. However, a digital broadcast standard may be different according to terrestrial, satellite, or cable propagation even in a single area. Even for terrestrial broadcast, many channels may use different modulation schemes upon occasion. In addition, a user in one area may want to receive a terrestrial or satellite broadcast signal forwarded from another area using a different standard than the user's area. As described above, when a user wants to view a plurality of broadcasts that have been modulated using different schemes on a single digital broadcast receiver, the digital broadcast receiver must have known all modulation schemes or the user needs to manually designate all of the modulation schemes. However, many broadcasting stations may use diverse modulation schemes and a single broadcasting station may use different modulation schemes according to a type of content. Accordingly, it actually may not be possible for the digital broadcast receiver to know all modulation schemes for individual broadcast signals in advance.
Therefore, if a transmitter transmits digital broadcast signals using diverse modulation schemes according to equipment characteristics, a digital broadcast receiver needs to search diverse demodulation schemes and correctly catch the broadcast signals for channels. Accordingly, a method of efficiently selecting a correct demodulation schemes for a digital broadcast signal having unknown modulation is desired.